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Vulnerabilities

Vulnerability · CVE-2026-42221

Nginx UI is a web user interface for the Nginx web server.

Published May 4, 2026 · catalog updated Jun 17, 2026 · nginx ui

Check if you run it

No confirmed exploitation is on record for CVE-2026-42221. EPSS is 1.60%. Act only if a listed version of nginx ui is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Critical9.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.60%
Remediation
Advisory link
Affected products
cpe nginxui/nginx ui

Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint is reachable without authentication, and the request-encryption flow only protects payload confidentiality in transit; it does not authenticate who is allowed to perform installation. A remote attacker who reaches the service before the legitimate operator can set the admin email, username, and password, causing permanent initial-instance takeover. This issue has been patched in version 2.3.8.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe nginxui/nginx uiversion unspecified

How to fix CVE-2026-42221

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-42221. EPSS is 1.60%. Act only if a listed version of nginx ui is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-306: Missing Authentication for Critical Function. EPSS 1.60%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Nginx security

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. May 4, 2026 · NIST NVD

    Detected

    Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint is reachable without authentication, and the request-encryption flow only protects payload confidentiality in transit; i

  2. Jun 17, 2026 · NIST NVD

    Updated

    Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint is reachable without authentication, and the request-encryption flow only protects payload confidentiality in transit; i

Sources

  • CVE.orgVulnerability recordCVE-2026-42221

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-42221

    30-day exploitation probability 1.6%

    first.org
  • NIST NVDVulnerability recordCVE-2026-42221

    Nginx UI is a web user interface for the Nginx web server. From version 2.0.0 to before version 2.3.8, an unauthenticated network attacker can claim the initial administrator account on a fresh nginx-ui instance during the first-run setup window. The public /api/install endpoint

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.